Over the past decade, deficits in prepulse inhibition (PPI) of the startle reflex have been reported in several clinical populations characterized by an inability to regulate internal and external stimulation including schizophrenia, obsessive-compulsive disorder, Huntington's Disease, and children with attention-deficit disorder. The prepulse inhibition deficits observed in these populations are interpreted as reflecting deficits in sensorimotor gating, a protective mechanism which momentarily prevents or attenuates extraneous reactions from interfering with ongoing cognitive processes. Despite the fact that sensorimotor gating is considered to be a fundamental aspect of cognition, and despite the wealth of clinical data, our ability to interpret prepulse inhibition deficits and understand their implications for cognition is severely limited by a lack of research examining the relationship between PPI and cognition in 'normal' information processing. In order to fill this void, the goal of the proposed research is to clarify the effects of selective and nonselective attentional processes on PPI by examining four distinct ways in which attention may influence PPI: nonspecific, modality specific, stimulus specific, or demand specific. Together, the results of these experiments will increase our understanding of the cognitive significance of prepulse inhibition, which in turn may shed light on how best to interpret the prepulse inhibition deficits observed in schizophrenia and other clinical populations. In addition, documenting the relationship between prepulse inhibition and cognitive processing will have important implications both for the development of cognitive theory, as well for designing future clinical applications of the prepulse inhibition measure.